Superhydrophobic powder coatings

ABSTRACT

A superhydrophobic coating, comprises a superhydrophobic powder with superhydrophobic particles having a three dimensional nanostructured surface topology defining pores, and a resin. The superhydrophobic particles are embedded within the resin and the resin does not fill the pores of the superhydrophobic particles such that the three dimensional surface topology of the superhydrophobic particles is preserved. A precursor powder for a superhydrophobic coating and a method for applying a superhydrophobic coating to a surface are also disclosed.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH

This invention was made with government support under contract No.DE-AC05-000R22725 awarded by the U.S. Department of Energy. Thegovernment has certain rights in this invention.

FIELD OF THE INVENTION

This invention relates to superhydrophobic materials, and moreparticularly to superhydrophobic coatings.

BACKGROUND OF THE INVENTION

Superhydrophobic coatings are typically only superhydrophobic at thecoating's outer surface. Once the outer surface is abraded away, thesurface is no longer superhydrophobic. This loss of superhydrophobicityis due to the superhydrophobic particles or structure being removed fromthe surface. Particles that are beneath the surface generally have theirnanopores and nanotextured surfaces clogged with the underlying coatingmaterial.

In a standard electrostatic powder spraying process, dry resin powder,is electrostatically sprayed onto a given electrically groundedsubstrate. The electrically charged dry powder adheres to the groundedsubstrate by electrostatic forces. When the dry resin powder is cured,it becomes well bonded to the substrate.

SUMMARY OF THE INVENTION

A superhydrophobic coating can include a superhydrophobic powder withsuperhydrophobic particles having a three dimensional nanostructuredsurface topology defining pores, and a resin. The superhydrophobicparticles can be embedded within the resin. According to certainembodiments, the resin does not completely fill the pores of thesuperhydrophobic particles, such that the three dimensional surfacetopology of the superhydrophobic particles is preserved.

The superhydrophobic particles can comprise a hydrophobic coating. Thehydrophobic coating can conform to the surface of the superhydrophobicparticle so as to preserve the nanostructured surface topology of theparticle. The superhydrophobic particle can comprise a diatomaceousearth particle. Diatomaceous earth particles have a nanostructuredsurface topology. When, according to various embodiments, a diatomaceousearth particle is coated with a hydrophobic coating, the diatomaceousearth particle can retain its nanostructured surface topology even afterbeing coated with the hydrophobic coating. According to variousembodiments, any or all of the super hydrophobic particles can have aporous core. The porous core of the superhydrophobic particles can behydrophilic. Diatomaceous earth is an example of a porous core that isnaturally hydrophilic. The porous core of the superhydrophobic particlescan be a silicate. The silicate can be etched to provide thenanostructured surface topology.

The resin into which the superhydrophobic particles are embedded can behydrophobic. A variety of polymers can be used as the resin. As usedherein, the term “resin” means any solid or liquid synthetic ornaturally occurring organic polymer and is not limited to materialsobtained from naturally occurring exudations from certain plants.

The pore volume of the superhydrophobic particle can be less than 50%filled by the resin. The diameter of the superhydrophobic particle canbe between 0.1-20 μm or between 1 and 20 μm. The diameter of thesuperhydrophobic particles can be between 10-20 μm. For purposes of thepresent application, the term “pore volume” refers to a fraction of thevolume of voids over the total volume of a particle. The term “porevolume” as used herein means the same as “porosity” or “voiddiffraction.” The pore volume can be expressed as either a fraction,between 0 and 1, or as a percentage, between 0 and 100%. The pore volumeof a particle can be measured by any known method including directmethods, optical methods, computed tomography methods, imbibitionmethods, water evaporation methods, mercury intrusion porosimetry, gasexpansion methods, thermoporosimetry, and cryoporometric methods.

The ratio of superhydrophobic particles to resin can be between 1:4 and1:20 by volume, between 1:5 and 1:7 by volume, between 1:1 and 1:4 byvolume, or between 1:1.5 and 1:2.5 by volume. For example, the ratio ofsuperhydrophobic particles to resin can be about 1:6 by volume or about1:2 by volume.

A precursor powder for a superhydrophobic coating can include asuperhydrophobic powder having superhydrophobic particles and aplurality of resin particles. The superhydrophobic particles have athree dimensional surface topology comprising pores. The resin particlescan include a resin material, which is capable, when cured, ofsurrounding and embedding the superhydrophobic particles, while notcompletely filling the pores of the superhydrophobic particles.

The diameter of the resin particles can be between 1-100 μm. Accordingto certain embodiments, the diameter of the resin particles can belarger than the pore size of the superhydrophobic particles, butgenerally not more than 20 times the diameter of the superhydrophobicparticles. According to certain embodiments, the diameter of the resinparticles can be larger than the pore size of the superhydrophobicparticles, but generally not more than 4 times the diameter of thesuperhydrophobic particles. The diameter of the resin particles can belarger than average pore size of the superhydrophobic particles, butgenerally not more than 10 times the diameter of the superhydrophobicparticles. According to other embodiments, the diameter of the resinparticles can be larger than average pore size of the superhydrophobicparticles, but generally not more than 2 times the diameter of thesuperhydrophobic particles.

A method for applying a superhydrophobic coating to a surface caninclude the steps of providing a precursor powder for a superhydrophobiccoating. The precursor powder can have a plurality of superhydrophobicparticles. The superhydrophobic particles can have a three dimensionalsurface topology comprising pores. The precursor powder also can includea plurality of resin particles. The resin particles can include a resinmaterial that is capable, when cured, of surrounding and embedding thesuperhydrophobic particles within the resin, but not completely fillingthe pores of the superhydrophobic particles. The precursor powder can beapplied to the surface. The resin can be cured to bond the resin to thesurface and to surround and/or to embed the superhydrophobic particlesin the resin.

The resin can be hydrophobic. The superhydrophobic particle can includea porous core material and a hydrophobic coating. The hydrophobiccoating can conform to the surface of the porous core material so as topreserve the nanostructured surface topology. The porous core materialcan be hydrophilic.

The porous core material can include a silicate. The silicate can beetched to provide a nanostructured surface topology. The porous corematerial can include diatomaceous earth. The pore volume of thesuperhydrophobic particle can be less than 50% filled by the resin. Thediameter of the superhydrophobic particle can be between 0.1-20 μm orabout 1 μm. The diameter of the superhydrophobic particles can bebetween 10-20 μm. The ratio of superhydrophobic particles to resin canbe between 1:4 and 1:20 by volume or between 1:1 and 1:4 by volume. Theratio of superhydrophobic particles to resin can be between 1:5 and 1:7by volume or between 1:1.5 and 1:2.5 by volume. The ratio ofsuperhydrophobic particles to resin can be about 1:6 by volume or about1:2 by volume. A layer of resin particles can be applied to the surfaceprior to applying the precursor powder to the surface. The precursorpowder can be applied to the surface by an electrostatic sprayingprocess.

BRIEF DESCRIPTION OF THE DRAWINGS

There are shown in the drawings embodiments that are presently preferredit being understood that the invention is not limited to thearrangements and instrumentalities shown, wherein: FIGS. 1 a-1 f areframes from a video demonstrating the superhydrophobicity of an aluminumpower line coated according to one embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

According to various embodiments a superhydrophobic coating can includea superhydrophobic powder with superhydrophobic particles and a resin.The superhydrophobic particles can have a three dimensionalnanostructured surface topology defining pores. The superhydrophobicparticles can be embedded within the resin, such that at least some ofthe superhydrophobic particles are completely enveloped by or surroundedby the resin. As used herein the term “embedded” means to enclose firmlyin a surrounding mass. The term “embedded” therefore includes not onlyparticles that are completely surrounded or enveloped by the resin butalso particles that are only partially enveloped, enclosed, orsurrounded in the surrounded resin. According to various embodiments, asuperhydrophobic coating can include a plurality of superhydrophobicparticles that includes some completely embedded particles and somepartially embedded particles. The completely embedded particles resideentirely within a resin layer such that they are surrounded on all sidesby resin. The partially embedded particles have portions of theirsurface area protruding beyond the resin layer's surface. Theprotruding, partially embedded, particles can impart superhydrophobicityto the surface of the coating. The completely embedded particles allowthe coating to remain superhydrophobic even after the surface of thecoating is abraded or sanded away. When the surface of the coating isabraded or sanded away some or all of the partially embedded particlescan be removed, but some or all of the completely embedded particles canbe exposed at the surface of the coating. The exposed particles can thenfunction to impart superhydrophobicity to the surface of the coating.

One reason that the completely embedded particles are able to maintaintheir superhydrophobicity once they are exposed to the surface aftersanding or abrading is that despite being completely embedded within theresin, the resin does not completely fill the pores or completely coverthe superhydrophobic particles. Since the resin does not completely fillthe pores or completely cover the superhydrophobic particles, the threedimensional surface topology of the superhydrophobic particles ispreserved. The resin can be capable of being melted and blended with thesuperhydrophobic (SH) particles without completely filling the pores ofthe superhydrophobic particles and/or without covering all of thenanotextured surfaces of the superhydrophobic particles. According tocertain embodiments, the superhydrophobic particles can repel the resinto preserve a volume of air within the porous core of eachsuperhydrophobic particle. The degree to which the resin does fill thepores of the superhydrophobic particles shall be defined in more detailhereinafter.

Various embodiments describe how to modify existing electrostatic spraypowder coating techniques such that the resulting coating iswell-bonded, durable, and superhydrophobic (SH). Various embodimentscombine dry powder resins with superhydrophobic, nano-textured amorphoussilica powder to form a well-bonded coating that is bothsuperhydrophobic at the surface and is still superhydrophobic when theouter surface is abraded away, for example, by sending the outersurface.

Additional embodiments relate to a precursor powder comprising superhydrophobic particles and resin particles.

Superhydrophobic Particles

Each of the superhydrophobic particles can comprise a hydrophobiccoating. The hydrophobic coating can conform to the surface of eachsuperhydrophobic particle, so as to preserve the nanostructured surfacetopology.

Any or all of the superhydrophobic particles can include a porous coreand/or a porous core material. The porous core and/or the porous corematerial can be hydrophilic. The porous core and/or the porous corematerial of the superhydrophobic particles can be a silicate. Thesilicate can be etched to provide the nanostructured surface topology.According to some embodiments the superhydrophobic particle can compriseone or more diatomaceous earth particles. The surface chemistry of theporous core and/or the porous core material can be changed fromhydrophilic to hydrophobic by the application of a hydrophobic coating.The hydrophobic coating can conform to the surface of the porous corematerial, so as to preserve the nanostructured surface topology.

The diameter of any or all of the superhydrophobic particles and/or theaverage diameter of the superhydrophobic particles can be within a rangehaving a lower limit and/or an upper limit. The range can include orexclude the lower limit and/or the upper limit. The lower limit and/orupper limit can be selected from 0.05, 0.1, 0.5, 1, 1.5, 2, 2.5, 3, 3.5,4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5, 9, 9.5, 10, 10.5, 11, 11.5, 12,12.5, 13, 13.5, 14, 14.5, 15, 15.5, 16, 16.5, 17, 17.5, 18, 18.5, 19,19.5, 20, 20.5, 21, 21.5, 22, 22.5, 23, 23.5, 24, 24.5, and 25 μm at oneatmosphere pressure. For example, according to certain preferredembodiments, the diameter of any or all of the superhydrophobicparticles and/or the average diameter of the superhydrophobic particlescan be from 0.1-20 μm, from 1-20 μm, or from 10-20 μm.

The pore volume of any or all of the superhydrophobic particles and/orthe average pore volume of the superhydrophobic particles can be withina range having a lower limit and/or an upper limit. The range caninclude or exclude the lower limit and/or the upper limit. The lowerlimit and/or upper limit can be selected from 0.01, 0.02, 0.03, 0.04,0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.11, 0.12, 0.13, 0.14, 0.15, 0.16,0.17, 0.18, 0.19, 0.2, 0.21, 0.22, 0.23, 0.24, 0.25, 0.26, 0.27, 0.28,0.29, 0.3, 0.31, 0.32, 0.33, 0.34, 0.35, 0.36, 0.37, 0.38, 0.39, 0.4,0.41, 0.42, 0.43, 0.44, 0.45, 0.46, 0.47, 0.48, 0.49, and 0.5 ml/g. Forexample, according to certain preferred embodiments, the pore volume ofany or all of the superhydrophobic particles and/or the average porevolume of the superhydrophobic particles can be 0.1-0.3 ml/g.

The surface area of any or all of the superhydrophobic particles and/orthe average surface area of any or all of the superhydrophobic particlescan be within a range having a lower limit and/or an upper limit. Therange can include or exclude the lower limit and/or the upper limit. Thelower limit and/or upper limit can be selected from 0.5, 1, 5, 10, 15,20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100,105, 110, 115, and 120 m²/gm. For example, according to certainpreferred embodiments, the surface area of any or all of thesuperhydrophobic particles and/or the average surface area of any or allof the superhydrophobic particles can be 1-100 m²/gm.

Differentially etched spinodal superhydrophobic powders are described indetail in U.S. Pat. No. 7,258,731 to D'Urso et al., issued on Aug. 21,2007, which is hereby incorporated by reference in its entirety, andconsists of nano-porous and nanotextured silica (once the borate hasbeen etched away). Such differentially etched spinal superhydrophobicpowders can be employed as the superhydrophobic particles according tovarious embodiments.

Superhydrophobic diatomaceous earth (SHDE) is described in detail U.S.Pat. No. 8,216,674 to Simpson et al., issued on Jul. 10, 2012) , whichis hereby incorporated by reference in its entirety. Suchsuperhydrophobic diatomaceous earth particles can be employed as thesuperhydrophobic particles according to various embodiments

Resin

According to various embodiments, the resin can be hydrophobic. Onexample of a suitable hydrophobic resin is fluorinated ethylenepropylene (FEP). Other embodiments can employ Ultra-violet (UV) curableresins, thermoset resins, and thermoplastic. UV curable resins areparticularly preferred for certain purposes, because they can allow forthe coating of various thermal sensitive substrates, such as plastics,waxes, or any material that might melt or soften at the curingtemperature used for other resins. According to certain embodiments, itcan be advantageous to use hydrophobic resins (like FEP) ofelectrostatic powder coat resins commercially available including,thermal set resins, thermal plastic resins, and UV curable resins.Combinations of various types of resins can also be employed.

Resins can include, but are not limited to, polypropylene; polystyrene;polyacrylate; polycyanoacrylates; polyacrylates; polysiloxanes;polyisobutylene; polyisoprene; polyvinylpyrrolidone; epoxy resins,polyester resins (also known as TGIC resins), polyurethane resins,polyvinyl alcohol; styrene block copolymers; block amide copolymers;amorphous fluoropolymer, such as that sold by E. I. du Pont de Nemoursand Company (“DuPont”) under the TEFLON AF® trademark; acryliccopolymer, alkyd resin mixtures, such as those sold by Rohm and Haasunder the FASTRACK XSR® trademark, and copolymers and mixtures thereof.

The resins can include further components, including tackifiers,plasticizers and other components.

In general, the smaller the resin powder grain size, the more uniformthe superhydrophobic powder dispersion. The same is true for thesuperhydrophobic powder grain size. It should be noted, however, thataccording to certain embodiments, if the resin grains become too small(<1 micron) it is more likely that the resins will begin to fill thepores of the superhydrophobic powder and cover up too much of thesurface texture of the superhydrophobic powder.

Superhydrophobic powder grains can have a diameter within a range havinga lower limit and/or an upper limit. The range can include or excludethe lower limit and/or the upper limit. The lower limit and/or upperlimit can be selected from 10, 15, 20, 30, 40, 50, 60, 70, 80, 90, 100,200, 300, 400, 500, 600, 700, 800, 900, 1000, 1500, 2000, 2500, 3000,3500, 4000, 4500, 5000, 5500, 6000, 6500, 7000, 7500, 8000, 8500, 9000,9500, 10000, 10500, 11000, 11500, 12000, 12500, 13000, 13500, 14000,14500, 15000, 15500, 16000, 16500, 17000, 17500, 18000, 18500, 19000,19500, 20000, 20500, 21000, 21500, 22000, 22500, 23000, 23500, 24000,24500, and 25000 nm. For example, according to certain preferredembodiments, superhydrophobic powder grains can have a diameter withinrange of from 20 nm to 20 microns, or from 100 nm to 15 microns.

The diameter of the resin particles can be within a range having a lowerlimit and/or an upper limit. The range can include or exclude the lowerlimit and/or the upper limit. The lower limit and/or upper limit can beselected from 0.01, 0.05, 0.1, 0.5, 1, 2, 3, 4, 5, 10, 15, 20, 25, 30,35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100, 105, 110, 115,and 120 μm. For example, according to certain preferred embodiments, thediameter of the resin particles can be between 1-100 μm.

The diameter of the resin particles can be larger than the pore size ofthe superhydrophobic particles by a factor within a range having a lowerlimit and/or an upper limit. The range can include or exclude the lowerlimit and/or the upper limit. The lower limit and/or upper limit can beselected from 1, 10, 100, 200, 300, 400, 500, 600, 700, 800, 900, 1000,1100, 1200, 1300, 1400, 1500, 1600, 1700, 1800, 1900, 2000, 2100, 2200,2300, 2400, 2500, 2600, 2700, 2800, 2900, 3000, 3100, 3200, 3300, 3400,3500, 3600, 3700, 3800, 3900, 4000, 4100, 4200, 4300, 4400, 4500, 4600,4700, 4800, 4900, and 5000. For example, according to certain preferredembodiments, the diameter of the resin particles can be larger than thepore size of the superhydrophobic particles by a factor within a rangeof from 1 to 5000. The resin particles could be as small as the silicapore size (˜20 nm pore size) and as large as 5000 times as large as thepores (i.e. 100 microns).

The diameter of the resin particles can be larger than the diameter ofthe superhydrophobic particles by a factor within a range having a lowerlimit and/or an upper limit. The range can include or exclude the lowerlimit and/or the upper limit. The lower limit and/or upper limit can beselected from 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.1, 1.2,1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7,2.8, 2.9, 3, 3.1, 3.2, 3.3, 3.4, 3.5, 3.6, 3.7, 3.8, 3.9, 4, 4.1, 4.2,4.3, 4.4, and 4.5. For example, according to certain preferredembodiments, the diameter of the resin particles can be larger than thediameter of the superhydrophobic particles by a factor within a range offrom 0.1 to 4.

According to some embodiments, the diameter of the resin particles canbe larger than the pore size of the superhydrophobic particles butgenerally not more than 20 times the diameter of the superhydrophobicparticles. According to other embodiments the diameter of the resinparticles can be larger than average pore size of the superhydrophobicparticles but generally not more than 10 times the diameter of thesuperhydrophobic particles.

Composition of the Superhydrophobic Coating

The ratio of superhydrophobic particles to resin in the superhydrophobiccoating, by volume can be selected from 1:1, 1:1.25, 1:1.5, 1:1.75, 1:2,1:2.25, 1:2.5, 1:2.75, 1:3, 1:3.25, 1:3.5, 1:3.75, 1:4, 1:4.25, 1:4.5,1:4.75, 1:5, 1:5.25, 1:5.5, 1:5.75, 1:6, 1:6.25, 1:6.5, 1:6.75, 1:7,1:7.25, 1:7.5, 1:7.75, 1:8, 1:8.25, 1:8.5, 1:8.75, 1:9, 1:9.25, 1:9.5,1:9.75, 1:10, 1:10.25, 1:10.5, 1:10.75, 1:11, 1:11.25, 1:11.5, 1:11.75,1:12, 1:12.25, 1:12.5, 1:12.75, 1:13, 1:13.25, 1:13.5, 1:13.75, 1:14,1:14.25, 1:14.5, 1:14.75, and 1:15. For example, according to certainpreferred embodiments, the ratio of superhydrophobic particles to resinin the superhydrophobic coating can be between 1:1 and 1:10, by volume.The ratio of superhydrophobic particles to resin can be between 1:1.5and 1:5, by volume. The ratio of superhydrophobic particles to resin canbe about 1:4, by volume.

The pore volume of any or all of superhydrophobic particle that isfilled by the resin can be within a range having a lower limit and/or anupper limit. The range can include or exclude the lower limit and/or theupper limit. The lower limit and/or upper limit can be selected from0.1, 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18,19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36,37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54,55, 56, 57, 58, 59, and 60%. For example, according to certain preferredembodiments, the pore volume of any or all of superhydrophobic particlecan be less than 50% filled by the resin.

Superhydrophobic powder grains, like superhydrophobic diatomaceousearth, are generally much lighter than resin grains of comparable sizebecause of the superhydrophobic powder grain's high porosity and surfacearea. In addition, the superhydrophobic diatomaceous earth powder grainsdescribed in this invention are generally much smaller than the typicalresin grains. For instance, resin grain sizes typically vary from about30 microns to 100 microns in diameter, while superhydrophobicdiatomaceous earth typically varies from 0.5 microns to 15 microns indiameter. This means that equal volumes of superhydrophobic diatomaceousearth and resin powder consist of considerably more SHDE grains and willcontain much more resin by weight.

Precursor Powder

A precursor powder for a superhydrophobic coating comprises asuperhydrophobic powder having superhydrophobic particles and aplurality of resin particles. The superhydrophobic particles can eachhave a three dimensional surface topology comprising pores. The resinparticles can comprise a resin material, which, when cured, can becapable of embedding the superhydrophobic particles within the resin,but does not completely fill the pores of the superhydrophobicparticles.

Superhydrophobic silicon dioxide (silica) nanoparticles can have adiameter within a range having a lower limit and/or an upper limit. Therange can include or exclude the lower limit and/or the upper limit. Thelower limit and/or upper limit can be selected from 0.1, 0.5, 1, 2, 3,4, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85,90, 95, 100, 105, 110, 115, 120, and 125 nm. For example, according tocertain preferred embodiments, superhydrophobic silica nanoparticles canhave a diameter of from 1 nm to 100 nm. Superhydrophobic silicananoparticles are typically spherical or approximately spherical andhave diameters of less than 100 nm in size. The silica particles canhave a diameter that is as small as a few nanometers, but oftenconglomerate into compound particles microns in size.

The diameter of particle conglomerates can be within a range having alower limit and/or an upper limit. The range can include or exclude thelower limit and/or the upper limit. The lower limit and/or upper limitcan be selected from 100, 150, 200, 300, 400, 500, 600, 700, 800, 900,1000, 1100, 1200, 1300, 1400, 1500, 1600, 1700, 1800, 1900, 2000, 2100,2200, 2300, 2400, 2500, 2600, 2700, 2800, 2900, 3000, 3100, 3200, 3300,3400, 3500, 3600, 3700, 3800, 3900, 4000, 4100, 4200, 4300, 4400, 4500,4600, 4700, 4800, 4900, 5000, 5100, 5200, 5300, 5400, and 5500 nm. Forexample, according to certain preferred embodiments, the diameter ofparticle conglomerates can be from 200 nm to 5 microns.

Once the superhydrophobic particles and the resin particles are blendedto form the precursor powder, the precursor powder can be directlysprayed (electrostatically) onto a substrate (usually a metal).

The substrate can then be preheated to a temperature within a rangehaving a lower limit and/or an upper limit. The range can include orexclude the lower limit and/or the upper limit. The lower limit and/orupper limit can be selected from 75, 80, 85, 90, 95, 100, 105, 110, 115,120, 125, 130, 135, 140, 145, 150, 155, 160, 165, 170, 175, 180, 185,190, 195, 200, 205, 210, 215, 220, 225, 230, 235, 240, 245, 250, 255,260, 265, 270, 275, 280, 285, 290, 295, and 300 degrees Fahrenheit. Forexample, according to certain preferred embodiments, the substrate canthen be preheated to a temperature within a range of from 100 degreesFahrenheit to 250 degrees Fahrenheit. This temperature range cancorrespond to the low end of the curing temperature range. Thepreheating step can allow the substrate to approach the curingtemperature of the resin before the resin cures.

Once the substrate is within 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10 degreesFahrenheit of the curing temperature, the temperature can be elevated tothe normal curing temperature range, which can be within a range havinga lower limit and/or an upper limit. The range can include or excludethe lower limit and/or the upper limit. The lower limit and/or upperlimit can be selected from 225, 230, 235, 240, 245, 250, 255, 260, 265,270, 275, 280, 285, 290, 295, 300, 305, 310, 315, 320, 325, 330, 335,340, 345, 350, 355, 360, 365, 370, 375, 380, 385, 390, 395, 400, 405,410, 415, 420, 425, 430, 435, 440, 445, 450, 455, 460, 465, 470, 475,480, 485, 490, 495, and 500 degrees Fahrenheit. For example, accordingto certain preferred embodiments, once the substrate is within 10degrees Fahrenheit of the curing temperature, the temperature can beelevated to the normal curing temperature range, which can be from 250degrees Fahrenheit to 450 degrees Fahrenheit. Once at curing range, thetemperature can be held for a time period. The time period can be withina range having a lower limit and/or an upper limit. The range caninclude or exclude the lower limit and/or the upper limit. The lowerlimit and/or upper limit can be selected from 5, 6, 7, 8, 9, 10, 11, 12,13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, and30 minutes. For example, according to certain preferred embodiments, thetime period can be from about 10 to 15 minutes. Since the substrate istypically already at or near the curing temperature, this increase intemperature readily increases the substrate temperature and allows theresin to sufficiently bond to the substrate.

The superhydrophobic powder can be mechanically bonded to the resin,because the resin partially penetrates into its porous nanotexturedstructure during the curing process. If the powder work cured at thecuring temperature without waiting for the substrate to warm up, thethermal mass of the substrate and insulation attributes ofsuperhydrophobic particles, such as superhydrophobic diatomaceous earth,would prevent the substrate from heating up to the curing temperaturebefore the resin cured. The result would be an unbonded superhydrophobicresin film that would simply fall off the substrate.

Application Process

A method for applying a superhydrophobic coating to a surface caninclude the steps of providing a precursor powder for a superhydrophobiccoating. The precursor powder can have a plurality of superhydrophobicparticles. The superhydrophobic particles can have a three dimensionalsurface topology comprising pores. The precursor powder can also includea plurality of resin particles. The resin particles can include a resinmaterial that is capable, when cured, of embedding the superhydrophobicparticles within the resin, but not filling the pores of thesuperhydrophobic particles or completely covering the particle surface.The precursor powder is applied to the surface. The resin is cured tobond the resin to the surface and to embed the superhydrophobicparticles in the resin.

The precursor powder can be applied by a spray-on process.

The precursor powder can be applied by dipping a hot substrate into ablended resin/superhydrophobic powder that would cause the blend to coatand cure on the substrate. The hot substrate can be maintained at atemperature within a range having a lower limit and/or an upper limit.The range can include or exclude the lower limit and/or the upper limit.The lower limit and/or upper limit can be selected from 175, 180, 185,190, 195, 200, 205, 210, 215, 220, 225, 230, 235, 240, 245, 250, 255,260, 265, 270, 275, 280, 285, 290, 295, 300, 305, 310, 315, 320, 325,330, 335, 340, 345, 350, 355, 360, 365, 370, 375, 380, 385, 390, 395,400, 405, 410, 415, 420, 425, 430, 435, 440, 445, and 450 degreesFahrenheit. For example, according to certain preferred embodiments, thehot substrate can be maintained at a temperature in a range of 200degrees Fahrenheit to 400 degrees Fahrenheit for a time period. The timeperiod can be within a range having a lower limit and/or an upper limit.The range can include or exclude the lower limit and/or the upper limit.The lower limit and/or upper limit can be selected from 5, 6, 7, 8, 9,10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27,28, 29, and 30 minutes. For example, according to certain preferredembodiments, the time period can be from about 10 to 15 minutes.

Preheating the substrate can be important due to the thermal insulatingeffects of the superhydrophobic silica powder. The fact that the drypowder blend contains a thermally insulating silica powder (e.g. SHDE)means that it will likely be more difficult to get the substrate up to atemperature that promotes curing. If the substrate is prevented fromreaching the curing temperature in the allotted curing time (because ofthe SH silica powder blend) then the coating might not adequately bondto the substrate.

The same type of coating/curing can be done with a hot substrateengulfed on a cloud of swirling powder. In this embodiment, the hotsubstrate can be maintained at a temperature within a range having alower limit and/or an upper limit. The range can include or exclude thelower limit and/or the upper limit. The lower limit and/or upper limitcan be selected from 175, 180, 185, 190, 195, 200, 205, 210, 215, 220,225, 230, 235, 240, 245, 250, 255, 260, 265, 270, 275, 280, 285, 290,295, 300, 305, 310, 315, 320, 325, 330, 335, 340, 345, 350, 355, 360,365, 370, 375, 380, 385, 390, 395, 400, 405, 410, 415, 420, 425, 430,435, 440, 445, and 450 degrees Fahrenheit. For example, according tocertain preferred embodiments, the hot substrate can be maintained at atemperature in a range of 200 degrees Fahrenheit to 400 degreesFahrenheit.

There are many possible variations for depositing the superhydrophobicpowder. In a process having only one application step, the dry powderresin and superhydrophobic particles can be blended together. Thesuperhydrophobic particles can be superhydrophobic diatomaceous earth(SHDE), but other nanostructured superhydrophobic powders can be used,such as silica nanoparticles, and differentially etched spinodaldecomposed borosilicate glass powder. Mixtures of different types ofsuperhydrophobic particles are also possible.

A layer of resin particles can be applied to the surface prior toapplying the precursor powder to the surface. The precursor powder canbe applied to the surface by an electrostatic spraying process.

Rejuvenation Process

Various embodiments relate to a method of rejuvenating asuperhydrophobic surface. The superhydrophobic surface can be a surfaceaccording to any of the preceding embodiments. The super hydrophobicsurface can be prepared according to any of the preceding embodiments.For example, the super hydrophobic surface can comprise a resin; and aplurality of superhydrophobic particles. Each superhydrophobic particlecan have a three dimensional, nanostructured surface topology, defininga plurality of pores. At least a portion of the superhydrophobicparticles can be embedded within the resin or chemically bonded to theresin so as to be surrounded by the resin. According to variousembodiments, the resin does not fill the pores of the embeddedsuperhydrophobic particles such that the three dimensional surfacetopology of the superhydrophobic particles is preserved. The method ofrejuvenating a super hydrophobic surface can comprise of simply abradingthe superhydrophobic surface to expose the embedded superhydrophobicparticles.

Again, superhydrophobic powder grains, like superhydrophobicdiatomaceous earth, are generally much lighter than resin grains ofcomparable size because of the superhydrophobic powder grain's highporosity and surface area. In addition, the superhydrophobicdiatomaceous earth powder grains described in this invention aregenerally much smaller than the typical resin grains. For instance,resin grain sizes typically vary from about 30 microns to 100 microns indiameter, while superhydrophobic diatomaceous earth typically variesfrom 0.5 microns to 15 microns in diameter. This means that equalvolumes of superhydrophobic diatomaceous earth and resin powder consistof considerably more SHDE grains and will contain much more resin byweight.

When a drop of water is surrounded by superhydrophobic silica powdervery small powder grains can be somewhat sticky to the drop and canproduce a thin film of such powder grains on the drop's surface. Suchwater drops covered with SH silica are called “water marbles.” Thesewater marbles generally will not combine with each other because of therepulsive effects of the SH powder. The same effect can occur to thecuring powder resins according to various embodiments to form resinmarbles. Each resin marble can be covered with a plurality ofsuperhydrophobic particles. In some cases formation of resin marbles isdesirable. Resin marbles are typically unable to be bonded to thesubstrate or with other resin marbles. For other applications, formationof resin marbles should be avoided by limiting the amount ofsuperhydrophobic particles (for example, silica powder) blended with theresins.

To avoid or to reduce formation of resin marbles, the ratio ofsuperhydrophobic particles to resin in the superhydrophobic coating canbe selected from 1:1, 1:1.25, 1:1.5, 1:1.75, 1:2, 1:2.25, 1:2.5, 1:2.75,1:3, 1:3.25, 1:3.5, 1:3.75, 1:4, 1:4.25, 1:4.5, 1:4.75, 1:5, 1:5.25,1:5.5, 1:5.75, 1:6, 1:6.25, 1:6.5, 1:6.75, 1:7, 1:7.25, 1:7.5, 1:7.75,1:8, 1:8.25, 1:8.5, 1:8.75, 1:9, 1:9.25, 1:9.5, 1:9.75, 1:10, 1:10.25,1:10.5, 1:10.75, 1:11, 1:11.25, 1:11.5, 1:11.75, 1:12, 1:12.25, 1:12.5,1:12.75, 1:13, 1:13.25, 1:13.5, 1:13.75, 1:14, 1:14.25, 1:14.5, 1:14.75,1:15, 1:15.25, 1:15.5, 1:15.75, 1:16, 1:16.25, 1:16.5, 1:16.75, 1:17,1:17.25, 1:17.5, 1:17.75, 1:18, 1:18.25, 1:18.5, 1:18.75, 1:19, 1:19.25,1:19.5, 1:19.75, 1:20, 1:20.25, 1:20.5, 1:20.75, 1:21, 1:21.25, 1:21.5,1:21.75, 1:22, 1:22.25, 1:22.5, 1:22.75, 1:23, 1:23.25, 1:23.5, 1:23.75,1:24, 1:24.25, 1:24.5, 1:24.75, and 1:25 by volume. For example,according to certain preferred embodiments, the ratio ofsuperhydrophobic particles to resin in the superhydrophobic coating canbe between 1:8 and 1:15 by volume, corresponding to about 1:3 and 1:10by weight. The ratio of superhydrophobic particles to resin can bebetween 1:1.5 and 1:5 by volume or about 1:4, by volume.

Ratios of superhydrophobic particles to resin in the superhydrophobiccoating can also be expressed by weight. To avoid or to minimizeformation of resin marbles, the ratio of superhydrophobic particles toresin in the superhydrophobic coating can be selected from 1:1, 1:1.25,1:1.5, 1:1.75, 1:2, 1:2.25, 1:2.5, 1:2.75, 1:3, 1:3.25, 1:3.5, 1:3.75,1:4, 1:4.25, 1:4.5, 1:4.75, 1:5, 1:5.25, 1:5.5, 1:5.75, 1:6, 1:6.25,1:6.5, 1:6.75, 1:7, 1:7.25, 1:7.5, 1:7.75, 1:8, 1:8.25, 1:8.5, 1:8.75,1:9, 1:9.25, 1:9.5, 1:9.75, 1:10, 1:10.25, 1:10.5, 1:10.75, 1:11,1:11.25, 1:11.5, 1:11.75, 1:12, 1:12.25, 1:12.5, 1:12.75, 1:13, 1:13.25,1:13.5, 1:13.75, 1:14, 1:14.25, 1:14.5, 1:14.75, 1:15, 1:15.25, 1:15.5,1:15.75, 1:16, 1:16.25, 1:16.5, 1:16.75, 1:17, 1:17.25, 1:17.5, 1:17.75,1:18, 1:18.25, 1:18.5, 1:18.75, 1:19, 1:19.25, 1:19.5, 1:19.75, 1:20,1:20.25, 1:20.5, 1:20.75, 1:21, 1:21.25, 1:21.5, 1:21.75, 1:22, 1:22.25,1:22.5, 1:22.75, 1:23, 1:23.25, 1:23.5, 1:23.75, 1:24, 1:24.25, 1:24.5,1:24.75, and 1:25 by weight. For example, the ratio of superhydrophobicparticles to resin in the superhydrophobic coating can be from about 1:3to about 1:9 by weight.

The preferred ratios depend on both the resin grain sizes and thesuperhydrophobic powder grain sizes. For instance, if superhydrophobicparticles having an average size of 10 microns was employed inconjunction with a resin having an average size of 50 microns, apreferred ratio of superhydrophobic particles to resin could be about1:8 by weight. If the superhydrophobic particles were much smaller, forexample, 1.0 micron diameter, and the resin was 50 microns, a preferredratio of superhydrophobic particles to resin could be 1:20 by weight. Inother words, if the superhydrophobic particles have a smaller diameter,then on either a weight basis or on a volume basis much lesssuperhydrophobic would be needed to avoid or to reduce formation ofresin marbles.

EXAMPLES Example 1

DuPont's Vulcan Black thermal set dry resin powder was blended withsuperhydrophobic diatomaceous earth (SHDE) particles. This blend wasthen electrostatically sprayed onto an electrically grounded substrate(usually a metal). The silica-based powders accept and hold anelectrostatic charge very well, better in fact, than the dry resinpowders themselves. Once the blended powder was electrostaticallyattached to the grounded substrate, the substrate was heated in an ovenusing a temperature that is on the low end of the powder resin's curingtemperature range. For the thermal set Vulcan Black resin the curingtemperature was 320 degrees Fahrenheit, which is about 20 degreesFahrenheit less than a normal low temperature curing temperature. Ingeneral, the curing temperature can be 20 degrees Fahrenheit below thelowest manufacturer's suggested curing temperature.

SHDE acts as a slight thermal insulator. When blended SHDE is applied tothe substrate, it will tend to inhibit substrate heating. Therefore, itis necessary, when using thermal set or thermal plastic powder resins,to preheat the substrate before curing, in order to insure goodresin-to-substrate adhesion during curing. The preheating step consistsof heating the coated substrate to a temperature slightly less than thelow end of the resin curing temperature. A temperature of 20 degreesFahrenheit below the manufacturer's lowest recommended curingtemperature was employed. In the case of Vulcan Black (VB), a preheattemperature of 320 degrees Fahrenheit was used. The preheat temperatureis held for a suitable amount of time such as 10 minutes. Once thesubstrate was preheated the oven temperature was raised to the normalcuring temperature (400 degrees Fahrenheit for 20 minutes, for VB).

The heating of the substrate and precursor powder can be by any suitablemethod. Conductive or convective heating is possible, as is radiantheating, microwave (RF) heating, and possibly also nuclear heating couldbe used, among others. Since the substrate is already close to thecuring temperature, an increase in temperature at this point readilyincreases the metal substrate temperature and allows the resin tosufficiently bond to the substrate.

Example 2

In the second variation, a two powder application step process was used.The dry resin powder, according to example 1, was electrostaticallysprayed onto the substrate in a standard electrostatic powder coatprocess. Next, a SHDE/dry resin precursor powder blend was sprayed ontothe substrate. Once both powder layers are electrostatically adhered tothe substrate, the layers were cured together in the same manner asdescribed previously. This second method provided good bonding to thesubstrate and increases overall coating durability while maintaining ahigh quality superhydrophobic surface and some abrasion resistance.

While these two application variations and associated set of stepsreflect current processing steps, it is in no way to be considered theonly way to coat the substrate. The precursor powder can be used andincorporated into many other powder coat processes.

If the substrate is not preheated before exposing the coating to thecuring temperature, the thermal mass of the substrate and insulationattributes of SHP would inhibit the substrate from heating properly tothe curing temperature before the resin cures. The result would be anunbonded SHP/resin film that would simply fall off the substrate.

A key feature of this process is the fact that the SHP is not actuallychemically bonded to the curing resin. During the resin curing processthe flowing resin dose not completely “wet” the superhydrophobicparticles, such as superhydrophobic diatomaceous earth. In fact, thesuperhydrophobic particles actually can somewhat repel the curing resin.This keeps the pores of the superhydrophobic particles generallyunclogged and full of air. But, some of the curing resin does flow intothe porous nanotextured structure such as pores. Once cured, the resinthat went into the pores mechanically holds the SHP in place,effectively bonding the superhydrophobic particles to and below thesurface.

Results of Examples 1 and 2

Using the blended superhydrophobic powder coating techniques describedin examples 1 and 2; both aluminum and steel plates were successfullycoated along with small aluminum power-line segments.

Based on these results, it should be clear that any metal (especiallyelectrically conductive metals), can be coated. Additionally, by usingstandard powder coating techniques of applying a conductive primercoating, paper, wood, cloth, plastics, etc. have been successfullypowder coated and thus could be made superhydrophobic with ourenhancements to such powder coatings.

Example 3

Superhydrophobic diatomaceous earth (SHDE) was blended with threel parts(by weight) of DuPont's thermal set resin Vulcan Black (VB)of toelectrostatically coat a power line segment. First, the powerline waselectrostatically sprayed with VB. Then, a blend of VB and SHDE, havinga 3:1 volume ratio, was electrostatically sprayed onto the powerline.

The combined coatings were cured at 200 degrees Celsius for 30 minutes.The result was a well-bonded superhydrophobic surface that maintainedsuperhydrophobic behavior even when the outer layers were abraded away.A Taber abrasion test according to ASTM D 4060, showed superhydrophobicbehavior after as many as 400 (fully loaded) Tabor cycles.

Results from the Taber Abrasion test are summarized in Table 1.

TABLE 1 Contact Angle Taber Cycles with a drop of water 0 165° 10 160°50 158° 100 158° 200 155° 300 153° 400 151° 450 135°

FIGS. 1 a-1 f are still frames taken from a video showing water dropletsrolling off of the coated powerline. These still frames demonstrate thatthe powerline was successfully rendered superhydrophobic.

Example 4

A variety of powder blend combinations, comprising a resin and aplurality of superhydrophobic particles have been successfully made.These include polyester (TGIC) resins like Vulcan Black, Oil Black (FromDuPont), and Safety Yellow (from Valspar), epoxy resins like PCM90133Black Epoxy Powder from PPG, and fluoropolymer powder resins likePD800012 Powder Duranar AAMA2605 from PPG.

All of these resins were blended with SHDE and testing forsuperhydrophobic behavior. All of the above resins and associated blendsof SHDE were able to be bonded to a variety of substrates (glass, wood,and aluminum) and exhibited contact angles in excess of 150 degrees.Tabor abrasion testing was done on coated aluminum plates coated withall the about resin/SHDE blends. Superhydrophobicity was maintained onthese plates for Taber (minimal loading) cycles exceeding 100 cycles.

One powder blend combination comprised DuPont's thermal set resin VulcanBlack (VB) Resin and superhydrophobic diatomaceous earth (SHDE) atratios of 3:1, and 4:1. It was discovered that as the ratio ofResin:SHDE increases (i.e. lower concentrations of SHDE) the degree ofwater repellency (i.e. contact angle) decreases, but some enhanced waterrepellency (over the bare resin) is expected at all SHDE concentrations(even very low concentrations). At the other extreme (i.e. as Resin:SHDEratio approaches zero i.e. the blend is entirely SHDE), most of the SHDEpowder did not get bonded to the coating, except at the interface of theSHDE layer and the first resin application layer. The result is a verysuperhydrophobic surface without a great deal of durability. That is, asmall amount of abrasion will remove the surface bond

SHDE. Once that's removed, the surface is no longer superhydrophobic.

Based on these results it can be reasonably concluded that a blendcomprising as little as 5% SHDE by volume could result in goodsuperhydrophobic behavior (contact angles of >150 degrees). As theblended proportion of SHDE increases, water repellency increases. Theblending of SHDE with resin also creates a volumetric SH effect, in thatremoval of some coating material, by mild abrasion, exposes fresh (notfully clogged) SHDE material and thus the abraded surface remains SH.

Blends resulting in a good superhydrophobic behavior can have an amountof superhydrophobic diatomaceous earth within a range of from 1 to 90%by weight. Preferred blends can comprise from 10% to 30% SHDE by weightor from 10% to 20% SHP by weight. For purposes of this example the term“good superhydrophobic behavior” means that when the blend is applied toa substrate according to various embodiments the resulting superhydrophobic coating has a contact angle with a drop of water in a rangeof from 150 degrees to 175 degrees, and a roll-off angle in a range offrom 0.1 degree to 15 degrees.

Example 5

Ultraviolet (UV) curable powder resins could be applied and blended thesame way as thermal sets resins and thermal plastic resins except thatthe ultraviolet curable powder resins would use UV radiation instead ofheat to cure. Since the silica-based superhydrophobic powder, accordingto various embodiments, readily transmits ultraviolet radiation, therewould be no curing degradation encountered when blending SHDE with UVcurable powders. UV curing would require the UV radiation to penetratethe sprayed resin layers far enough to cure all the resin layers. Sincethe superhydrophobic powders, according to various embodiments, transmit(i.e. are non-absorbing) UV radiation, any UV radiation that would curethese resin layers that didn't contain superhydrophobic powders, wouldalso cure the same resin layers that do contain superhydrophobicpowders.

The foregoing description of the preferred embodiments of the inventionhas been presented for purposes of illustration. The invention is notlimited to the embodiments disclosed. Modifications and variations tothe disclosed embodiments are possible and within the scope of theinvention.

We claim:
 1. A superhydrophobic coating, comprising: a resin; and aplurality of superhydrophobic particles, wherein each superhydrophobicparticle has a three dimensional, nanostructured surface topology,defining a plurality of pores, wherein at least a portion of thesuperhydrophobic particles are embedded within the resin so as to besurrounded by the resin, and wherein the resin does not fill the poresof the embedded superhydrophobic particles such that the threedimensional surface topology of the superhydrophobic particles ispreserved.
 2. The superhydrophobic coating of claim 1, wherein the resinis hydrophobic.
 3. The superhydrophobic coating of claim 1, wherein thesuperhydrophobic particle comprises a hydrophobic coating, thehydrophobic coating conforming to the surface of the superhydrophobicparticle so as to preserve the nanostructured surface topology.
 4. Thesuperhydrophobic coating of claim 3, wherein the superhydrophobicparticle comprises a diatomaceous earth particle.
 5. Thesuperhydrophobic coating of claim 1, wherein the porous core ishydrophilic.
 6. The superhydrophobic coating of claim 1, wherein theporous core is a silicate.
 7. The superhydrophobic coating of claim 6,wherein the silicate is etched to provide the nanostructured surfacetopology.
 8. The superhydrophobic coating of claim 1, wherein the porevolume of the superhydrophobic particle is less than 50% filled by theresin.
 9. The superhydrophobic coating of claim 1, wherein the diameterof the superhydrophobic particle is between 1-20 μm.
 10. Thesuperhydrophobic coating of claim 1, wherein the diameter of thesuperhydrophobic particles is between 10-20 μm.
 11. The superhydrophobiccoating of claim 1, wherein the ratio of superhydrophobic particles toresin is between 1:1 and 1:10, by volume.
 12. The superhydrophobiccoating of claim 1, wherein the ratio of superhydrophobic particles toresin is between 1:1.5 and 1:5, by volume.
 13. The superhydrophobiccoating of claim 1, wherein the ratio of superhydrophobic particles toresin is about 1:4, by volume.
 14. A precursor powder for asuperhydrophobic coating, comprising: a plurality of superhydrophobicparticles having a three dimensional surface topology comprising pores;and a plurality of resin particles, the resin being capable when curedof embedding the superhydrophobic particles within the resin but notfilling the pores of the superhydrophobic particles.
 15. The precursorpowder for a superhydrophobic coating of claim 14, wherein the resinparticles are between 1-100 μm.
 16. The precursor powder for asuperhydrophobic coating of claim 14, wherein diameter of the resinparticles is larger than the pore size of the superhydrophobic particlesbut not more than 4 times the diameter of the superhydrophobicparticles.
 17. The precursor powder for a superhydrophobic coating ofclaim 14, wherein the diameter of the resin particles is larger thanaverage pore size of the superhydrophobic particles but not more than 2times the diameter of the superhydrophobic particles.
 18. A method forapplying a superhydrophobic coating to a surface, comprising the stepsof: providing a precursor powder for a superhydrophobic coating,comprising a superhydrophobic powder comprising superhydrophobicparticles, the superhydrophobic particles having a three dimensionalsurface topology comprising pores, and a plurality of resin particles,the resin being capable when cured of embedding the superhydrophobicparticles within the resin but not filling the pores of thesuperhydrophobic particles; applying the precursor powder to thesurface; and, curing the resin to bond the resin to the surface andembed the superhydrophobic particles in the resin.
 19. The method ofclaim 18, wherein the resin is hydrophobic.
 20. The method of claim 18,wherein the superhydrophobic particle comprises a porous core materialand a hydrophobic coating, the hydrophobic coating conforming to thesurface of the porous core material so as to preserve the nanostructuredsurface topology.
 21. The method of claim 18, wherein the porous corematerial is hydrophilic.
 22. The method of claim 18, wherein the porouscore material comprises a silicate.
 23. The method of claim 22, whereinthe silicate is etched to provide a nanostructured surface topology. 24.The method of claim 18, wherein the porous core material comprisesdiatomaceous earth.
 25. The method of claim 18, wherein the pore volumeof the superhydrophobic particle is less than 50% filled by the resin.26. The method of claim 18, wherein the diameter of the superhydrophobicparticle is between 1-20 μm.
 27. The method of claim 18, wherein thediameter of the superhydrophobic particles is between 10-20 μm.
 28. Themethod of claim 18, wherein the ratio of superhydrophobic particles toresin is between 1:1 and 1:4, by volume.
 29. The method of claim 18,wherein the ratio of superhydrophobic particles to resin is between1:1.5 and 1:2.5, by volume.
 30. The method of claim 18, wherein theratio of superhydrophobic particles to resin is about 1:2, by volume.31. The method of claim 18, wherein prior to applying the precursorpowder to the surface, a layer of resin particles is applied to thesurface.
 32. The method of claim 18, wherein the precursor powder isapplied to the surface by an electrostatic spraying process.
 33. Amethod of rejuvenating a superhydrophobic surface, the super hydrophobicsurface comprising a resin; and a plurality of superhydrophobicparticles, wherein each superhydrophobic particle has a threedimensional, nanostructured surface topology, defining a plurality ofpores, wherein at least a portion of the superhydrophobic particles areembedded within the resin so as to be surrounded by the resin, andwherein the resin does not fill the pores of the embeddedsuperhydrophobic particles such that the three dimensional surfacetopology of the superhydrophobic particles is preserved; the methodcomprising abrading the superhydrophobic surface to expose the embeddedsuperhydrophobic particles.